1. Field of the Invention
The present invention relates to a liquefied natural gas (LNG) transportation/distribution and vaporization management system, and in particular to a system that allows a transportation/distribution platform to transport/distribute and manage liquefied natural gas and a fuel cell module for vaporization of the liquefied natural gas and supply of natural gas.
2. The Related Arts
The resources of natural gas are one of the clean power generation fuels and energies that have been widely discussed throughout the whole world. Particularly, the natural gas can be generally completely combusted and the amount of the byproduct of carbon dioxide emitted is far less than the amount of carbon dioxide generated by a thermal power generation system based on energy from coals, making it a clean and environmentally friendly way of power generation and supply of energy that has been actively developed by countries around the world. Further, natural gas is also the primary energy for cooking and supplying of hot water for families. Thus, natural gas is an indispensable supply of energy for power generation and fuel resources for daily living and as such, the transportation/distribution, vaporization, and management of natural gas are of vital importance.
The primary transportation vehicle for transportation of liquefied natural gas is specifically constructed liquefied natural gas transportation vessels. The liquefied natural gas, after unloaded at a specific harbor, must be filled into a large storage tank built on an area of the harbor or constructed underground. An early-day liquefied natural gas transportation vessel may ship liquefied natural gas of a volume of around 120,000-140,000 m3 (approximately 50 thousand tons), which must be filled into a temporary storage tank of a large capacity of 100-200 thousand kiloliter, so that to supply natural gas, a complicated process of vaporization is applied to allow the vaporized gas to be pressurized and supplied through an extended length of natural gas supply pipeline to a large storage tank of a local gas company. The gas company then distributes, through gas distribution pipelines, the natural gas to resident users or downstream users. There are three known and commonly used ways of vaporization, of which the first one is ambient air vaporization (AAV), where air temperature of the surroundings is used to exchange heat with liquefied natural gas for vaporization. However, although the air temperature in for example a subtropic area or a tropic area may be above 0° C. (for example the average summer temperature of Taiwan being around 25° C. and the average winter temperature being around 15° C.), the temperature of liquefied natural gas is as low as −165° C., and this makes the efficiency of vaporization in this way very poor and rate of vaporization is low and is readily susceptible to environmental factors, such as temperatures of different seasons, temperature difference between daytime and nighttime, wind directions, and humidity, all these making the efficiency of vaporization even poorer. In addition, in the process of such a way of vaporization, sites adjacent to an inlet port of liquefied natural gas and heat exchange plates for vaporization may readily get frozen, which negatively affects the efficiency and rate of vaporization. Further, powerful fans must be installed to generate airflows of large amounts of air for such a way of vaporization. In addition to the installation expenditure, a large amount of electrical power must be consumed and an increased surface area is needed for a workshop operating such a way of vaporization. This is adverse to industrial utilization and economic value.
The second way of vaporization is open rack vaporization, where sea water from the sea where a liquefied natural gas unloading harbor is used and supplied to a heat exchanger for spraying so that the temperature of the sea water is used to achieve heat exchange for vaporization of liquefied natural gas. Similarly, although the average temperature of the sea water must be at least 5° C., it is readily affected by the environment and weather of the local area. Further, after heat exchange with the liquefied natural gas, the sea water must have a temperature that keeps the temperature difference between ingress and egress within a range of 5° C. according to most local regulations of environmental protection. Direct discharge of the sea water back to the sea would cause a severe impact on the marine creatures and ecology of the local sea area, this being not an operation mode acceptable for environmental protection. Further, such a process of using sea water as a heat exchange medium requires the sea water to be filtered first in order to remove impurities or oil contamination from the sea water, otherwise the sea water may readily get frozen in the heat exchanger. This makes the operation and installation costs high and also requires a large area of workshop for such an operation, making it adverse to industrial utilization and economic value.
The third way of vaporization is intermediate fluid vaporization, where liquids of other types of hydrocarbon compounds are used as a medium for a first stage of heat exchange with liquefied natural gas and sea water that is heated is used as a medium for a second stage of heat exchange. Although this is effective in improving the problem of sea water getting frozen in a process of vaporization through spraying the sea water, the two-stage process of heat exchange for vaporization requires complicated operations and more labor and time cost. In addition, hydrocarbon compound liquids, such as propane (C3H8) or butane (C4H10), must be pressurized and this requires additional consumption of electrical power and installation cost. Further, since sea water is used as a medium for heat exchange, the same issues of impurity of sea water and environmental protection of impact to marine creatures and ecology caused by variation of sea water temperature exist.
All the known ways of vaporization of liquefied natural gas discussed above suffer different problems and drawbacks. The process of transportation and vaporization of liquefied natural gas must be conducted in the specific harbor unloading area or a large storage tank and then the natural gas is supplied through an extended length of a supply pipeline to a local gas company or a plurality of gas tank trucks having a capacity of 10-15 tons is used to transport the natural gas, through a long way of surface roads, to downstream users. In addition to the high cost of transportation and distribution, the efficiency of transportation through the gas tank trucks is susceptible to influence caused by road conditions and weather. The elongated vaporization and poor transportation efficiency of liquefied natural gas may cause insufficient supply or delayed supply to the downstream users. In other words, vaporization may not be achieved timely to supply natural gas to the local gas company and the downstream users. Thus, the distribution of natural gas through a long process based on harbor unloading area or a large storage tank to an upstream supply pipeline to the local gas company makes it not possible to timely and flexibly supply natural gas and also requires an extremely large area of workshop, as well as a great amount of human labor for operation, monitoring, and management, making adverse to automatic management of workshop and facility. In addition, when the upstream gas supply pipeline is shut down due to for example damage and leaking, the supply of natural to the downstream gas company and users is affected. This causes undesired problems and drawbacks of transportation and distribution of natural gas.
Prior art patent documents are known. For example, Taiwan Patent No. 568863 discloses a liquefied natural gas vaporization technique that, similar to the prior art discussed above, uses sea water for vaporization, where a vessel cooling device (2), an underwater heat exchanger (21), and a vaporization device (23) made of a super stainless steel that are partly immersed in sea water to achieve vaporization of the liquefied natural gas carried in a transportation vessel. The same problems as those of the second and third ways of vaporization discussed above where sea water or sea water plus a fluid medium are used for vaporization exist. In addition, the vessel cooling device (2), the underwater heat exchanger (21), and the vaporization device (23) must be better treated for rusting protection or made of a better material. This increases the installation cost. Further, the transpiration and distribution of natural gas suffer the same problems as the third way of vaporization of being incapable of timely and flexibly supplying to the downstream users. In addition, the operation of vaporization covers a large range and thus, a large amount of human labor is needed for operation and monitoring. The operation area is hard to effectively managed and controlled.
Also, Taiwan Patent No. 489198 discloses a typical method and technique for vaporization of liquefied natural gas by using sea water to conduct heat exchange, which suffers the same problems and drawbacks of the conventional open rack vaporization of the second way discussed above. In addition, such a solution of transportation and distribution of liquefied natural gas is based on large-sized vessels and similarly, it is not possible to provide transportation/distribution and vaporization/supply of natural gas in a timely and flexible manner to the downstream gas companies and users.
Further, Taiwan Patent No. 197466 discloses vaporization and liquefied natural gas and power generation by using a gas turbine (GT), a pump (P1), four sets of heat exchangers (E1), (E2), (E3), and (E4), a complicated system of pipelines (1), (2a), (2b), (2c), (2d), (3a), and (3b), and an expansion turbine (X1). Such a structure of vaporization of liquefied natural gas is extremely complicated so that the cost is high and a large area of workshop is necessary, making it hard to manage and monitor. Again, it is not possible to build up at any desired location. Such a solution of transportation and distribution of liquefied natural gas still suffers the above-discussed problems of being not possible for timely and flexible vaporization and supply of natural gas and management being hard and requiring extra manpower. In addition, such a solution requires repeated pressurization and depressurization during vaporization through heating by using circulating water so that there is a great loss of thermal energy during the transmission thereof, whereby the heat-electricity conversion efficiency of the expansion turbine (X1) for power generation is very poor. In other words, the performance of power generation is poor, making it simply for embellishment and not possible to supply electrical power for the operation of the workshop. In addition, the solution requires a large amount of circulation of water for heat exchange and thus, the vaporization and power generation workshop must be built up in a site where a large supply of water is accessible, making it not possible to be constructed in a remote area where the supply of water and electricity is lacking or insufficient.
Further, Chinese Patent Publication No. CN104160130 and Japanese Patent Publication No. 2014-532833 disclose a solution using liquefied carbon dioxide (CO2) to serve as a primary medium for a liquefied natural gas vaporization system and a turbine generator (3) is involved, where a power turbine (2) and a liquefied CO2 pump (5) are operable to feed a combustion product flow (6) and a cooling CO2 recirculation flow (22) to generate electrical power. Similarly, the solution of the patent documents is a complicated structure of vaporization of liquefied natural gas and power generation, requiring a high cost of installation and occupying a large area of a workshop, so that it cannot be built up in any desired location and needs a large amount of manpower for operation, monitoring, and management, making it adverse to automatic management of workshop and facility. Such a solution of transportation and distribution of liquefied natural gas still suffers the problems and drawbacks of being not possible for timely and flexible vaporization and supply of natural gas. Again, the liquefied carbon dioxide flow and the fuel product flow involved in the solution of these patent documents are generally not materials allowing for repeated re-use for environmental protection. Leaking of such material would cause severe environmental pollution and damage to conservation of the environment, making it not possible for industrial uses in a large scale and being only available for specific industrial users, so that the use thereof is limited.